Radio transmitter



Nov. 27, 1945. YOUNG RADIO TRANSMITTER 2 Sheets-Sheet 1 Filed Feb. 9, 1944 FIG. 1.

RE INPUT w 50 6 .m M L NM m x II E M T6 m N/ T U aw l m 0 U m0 E N H O J ATTORNEY,

Nov. 27, 1945. J. E. YOUNG RADIO TRANSMITTER Filed Feb. 9, 1944 2 Sheets-Sheet 2 ATTORNEY Patented Nov. 27, 1945 UNITED STATES PATENT OFFICE 2,389,835 nsmo TRANSMITTER.

John E. Young, Mcrchantville, N. J., asslgnor to Radio Corporation of America, a corporation of Delaware Application February 9, 1944, Serial No. 521,633

" 13 Claims.

construction employing a: metallic panel main-.

tained at the same D.-C. potential as the associated vacuum tube stage and which supports the elements comprising the output tank and filter. This construction makes use of a-common radio frequency bypass condenser, thus eliminating the necessity for a multiplicity of bypass condensers which would ordinarily be required for the various network circuit elements, and improves the operation of the associated vacuum tube stage by reducing the tendency to the generation of parasitic oscillations.

Another advantage of this novel construction is that it enables the circuit to be fully effective in suppressing undesired harmonics produced by the associated vacuum tube stage.

A more detailed description of the invention follows in conjunction with the drawings wherein Figure 1 illustrates schematically a known type of high power radio transmitter;

Figure 2 illustrates the novel mechanical and electrical structure of the transmitter of the present invention; and

Figure 3 schematically illustrates the equivalent electrical circuit of. I the transmitter of Fig. 2.

Referring to the system of Fig. 1, which exemplifies known practice, there is shown that portion of a high power transmitter which couples a push-pull amplifier stage 2, 4 to a, suitable transmission line extending to a load such as an antenna. The vacuum tubes 2 and 4 are shown as triodes whose 'grids are coupled to opposite terminals of a parallel tuned circuit 2| to which is supplied radio frequency energy from a suitable input circuit. In practice, the radio frequency input circuit would include one or more is supplied through blocking condensers l5 and I! to a suitable transmission line coupling the power amplifier to the load.

' peak value above 7,500 volts.

A large portion of the capacity for pi network- A'is made up of the anode to cathode interelectrode tube capacities shown in dotted lines and labeled by the reference numerals 6, 8'. The interelectrode vacuum tube capacities 6, 8 are essential elements of the input capacity to the pi network A in the particular system shown. Coils l0 and I2 are removable plug-in coils for enabling the power amplifier tubes 2, 4 to be used with difierent frequency bands. Condensers l4, it are motor driven variable multi-plate air condensers. Condensers I8, 20, 22 and 24 are fixed" condensers of adequate rating and may, if desired, be of the mica or sulphur filled'type.

The alternating voltage at the anodes of the tubes 2, 4 may be of the order of 6,000 or 7,000 volts, and this alternating voltage is reduced at points 26, 28 to the order of only 1,500 volts-due to the impedance transfer property of the network A. Anode polarizing potential is supplied to the anodes over lead- 36, which connects to the midpoint of choke coil 30 connected across the two sides of the network B. This D.- C. potential may be of the order of 6,000 volts. With the arrangement shown, it is not possible to directly connect the junction points between condensers l4 and I6 and between condensers 22 and 24 to ground unless these condensers are built to withstand both the direct current and the alternating voltages to which the circuits are subjected. With the voltage values indicated above, the combined directcurrent' and altemating voltages across condensers 22 and 24 and across condensers I4 and It; would amount to a To enable these condensers to withstand this high peak value of voltage entails relatively costly construction. In the alternative, these condensers l4, I6, 22, 24 can be designed to withstand only the alternating voltage, in which case there would be required the additionalbypass grounding condensers 32- and 34-, the latter, in turn, designed to withstand the 6,000 volts of anode polarizing potential lmpressed onv the circuit by lead 36. In this last case, which is the situation illustrated in the signed for high voltage rating and therefore are costly or, in the alternative, they require a sepa-: rate bypass condenser 40 connected to ground. The use of condenser 40 also gives rise to parasitics and requires additional resistors H. l3 for the same purpose described above in connection with resistors 1, 9.

By way of further explanati n, bypass or grounding condenser 32, 34 and 40 set up parasitics because they resonate with the inductance of the leads to the various circuit elements. These grounding condensers are further obiectionable since they serve to partially suppress and nullify the effectivenes of the pi networks A and B. This follows because of the fact that the harmonics generated by the tubes 2 and 4 have a tendency to remain in and flow through the various condenser leads rather than be confined to 'the pi networks. It is for this reason that the inductance in the leads to the grounding condensers act to nullify the desired. short, low impedance paths to ground from the junction points of the network tuning capacitors #4, l8; I8, 20; and 22. 24.

The foregoing difllculties and objectionable features in the known circuit of. Fi 1' are overcome in the present invention by the construction shown in Fig. 2. Throughout all figures of the drawings, the same parts are designated by the same reference numerals.

In Fig. 2 there is provided a metallic mountina or support panel or plate 50 wh ch is arran ed vertically and serves to support t e variou circuit components of the pi networks A and B as modified in the manner described hereinafter. Panel 50 is insulatingly Spaced from a metallic vertically arranged around plate 10 b means of stand-off insulators 54. 56. Four of these insulaparallel relation on opposite sides of the network. The condensers l4 and I t serve both as output capacitors for the network A and as input capacitors for the network B. Condensers I8, 20 are padding condensers to extend the frequency range. The inductors Ill and 62 are supported by stand-oi! insulators 6|, 64 and-their terminals on insulators 64 are connected to the ungrounded terminals of harmonic attenuator condensers 22, 24. Condensers 22 and 24 are fixed and their other terminals are directly connected to the metallic panel 50. The high positive D.-C. potential for the anodes of the vacuum tubes 2 and 4 is supplied from source +B through lead 36 which connects to the midpoint of choke coil 30, the latter, in turn, being positioned across the condensers 22 and 24, as shown. The center tap of choke coil is connected to the metallic panel 50 through a resistor 52, thus maintaining the panel 50 at the same high D.-C. potential as the anodes of vacuum tubes 2 and 4. Blocking condensers l5 and H, which couple the B network to the load, are supported on stand-oil insulators 65 and 61.

A better understanding of the operation of Fig. 2 may be had by referring to the equivalent electrical circuit diagram of Fig. 3. It will be seen from an inspection of Fig. 3 that the metallic panel is maintained at the high positive D.-C. anode potential and that no current flows through resistor 52 under steady state conditions because the supporting panel 50 is insulatingly supported from ground for unidirectional currents by virtue of the stand-oil insulators 54, 56. Be-

tors are provided, as shown. to support the plate 50 from 'the ground plate '10. Panel 50 is maintained at the high 6.000 volts D.-C. anode potential supplied through lead 36. and this panel is grounded for radio frequencies by means of a common bypass condenser 68. Thi common bypass condenser not only grounds the panel 50 for radio frequency ener y. but also replaces the various grounding condensers 32. 34 and 40. shown in Fig. 1, and eliminated from the circuit of Fi 2.

'For reasons which will appear in more detail later, the insulators and condensers supportin the circuit elements on the panel 50 are designed only to withstand the alternating component of the radio frequency voltages in the circuit. The stand-01f insulators for the panel 50 are relatively inexpensive. few in number. and need, in general, withstand only the D.C. voltage applied to the common supporting panel 50.

The vacuum tubes 2 and 4 are shown mounted in the rear of the panel 50. and the anode connections from these two tubes extend through holes 69 in the panel 50 for connection to the plug-in coils l0, I2. The plug-in coils l0, 12 are supported by means of stand-off insulators 58, 59. The variable condensers l4, .16. respectively, are connected at one terminal to the metallic panel 50 and at the other terminal to the coils l0 and I2. These condensers are here shown as bein multi-plate air condenser which are variable and driven by a motor arrangement not shown. Those terminals of condensers l4 and I6 which are directly connected to the coils l0 and I2 are also connected through fixed condensers I8, 20 to radio frequency ground plate 50. It will thus be seen that the condensers l8 and I4 are in parallel relation while the condensers 20 and it are also in cause of the fact that the anode polarizing potential from lead 36 appears both on the panel 50, which is connected to one side of each of condensers l4, l6, I8, 20 and also appears on the other side of these same condensers, it will be apparent that there is no D.-C. potential difference across these condenser and there is no necessity to design these condensers to withstand a high D.-C. potential, as was the case in Fig. 1. These condensers l4, l6, l8 and 20, however, need be designed to withstand only the radio frequency components of the voltages in the circuits as they arise at the supporting points corresponding to the terminals of inductors l0, l2 and B0, 62. It should be noted that the system of Figs. 2 and 3 eliminates the necessity for the use of grounding condensers 32, 34 and 40 of Fig. 1 and also eliminates the necessity for the use of resistors 1,9, M and 13.

In one embodiment of the invention successfully tried out in practice, the system of Fig. 2 formed an essential part of a 7.5 kw. transmitter operating in the range from 2.5 to 25 megacycles, depending upon the choice of inductors and capacitors. The anode D.-C. potential supplied to the choke 30 was of the order of 6,000 volts. The vacuum tubes 2 and 4 were RCA 889R tubes having an elongated anode supplied with fins for air cooling. The radio frequency input to the grids of the push-pull tubes 2 and 4 was supplied from a highly stable low power oscillator generating oscillations of 2.5 megacycles. Several stages of amplification and, if desired, multiplication were provided between the output of the oscillator and the input of the power amplifier 2, 4.

It should be understood that various modifications may bemade in the system of the invention without departing from the spirit and scope thereof. For example. the mounting panel 50 can be designed to have sufficient area and by suitable spacing relative to the ground plate 10.

V eluding a vacuum tube stage-and a utilization circuit, a network in the output of said stage, said network having a plurality of condensers thereacross, a direct connection between one terminal of one of said condensers and a termina of another of said condensers, said direct connection comprising a mounting panel for supporting said network, a source of anode polarizing potential and means for supplying said potential to said stage through said network, a directcurrent connection from said source to said panel, saidpanel being effectively bypassed to a point of zero radio frequency potential forenergy of the operating frequency.

2. High power high frequency apparatus incuit, a network coupling the output electrode of said stage to said utilization circuit, said network including a coil an a pair of condensers parallelly connected, one terminal of said parallel combination being connected to one terminal of said coil, the other terminal of said parallel combination being connected to a metallic mountingpanel, stand-oil insulating means supporting said coil from said panel, a source of polarizing potential for the output electrode of said stage connected to one terminal of said coil, a direct current connection from said source to said panel, and means for by-passing said panel to a surface of zero radio frequency potential for energy of the operating frequency.

3. A high power transmitter comprising a triode vacuum tube, a network comprising a coil having one terminalconnected to the anode of said tube and the other terminal coupled to a utilization circuit, the interelectrode capacity of said tube constituting the input capacity of said network, a, metallic panel supporting said coil by insulating means positioned between the coil and panel, an output capacitor for said network comprising a condenser one'elctrode of which is connected to said last terminal of said coil and the other electrode of which is connected to said panel, a source of direct current potential, a connection from the positive terminal of said source to said coil for supplying polarizing potential to the anode of said tube, and a direct current connection from said source to said panel, whereby the electrodes of said condenser have substantially the same direct current potential applied thereto, said panel being by-passed to ground for energy of the operating frequency.

4. A high power transmitter comprising a push I pull amplifier stage, including a pair of vacuum tubes, a source of radio frequency energy coupled to the input electrodes of said tubes, a network including a pair of coils connected to different output electrodes of said tubes and coupling said tubes to a utilization circuit, a pair of condensers connected in series across those terminals of said coils farthest removed from said output electrodes, a metallic panel supporting the compoizing potential forthe output electrodes of said tubes, separate direct current connections from said source to said coils and panel, and a single by-pass condenser coupling said panel to a surface of zero radio frequency potential.

5. A high power radio transmitter comprising a push-pull amplifier stage comprising a pair of each of said networks including an inductor coil eluding a vacuum tube stage and a utilization cirsurface, a source'of anode direct current polariz-' ing potential for said vacuum tubes connected to the two sides of that pi network nearest the load, and a direct current connection from said source of polarizing potential to said common metallic surface, whereby said condensers need only be able to withstand the alternating voltage from said amplifier stage, said surface being by-passed to ground for energy of the operating frequency.

6. A radio transmitter including a vacuum tube stage, a utilization circuit therefor, a pi network coupling the output electrode of said stage and said utilization circuit, said network including a coil and a condenser at each end of said coil, a metallic surface connecting together one terminal of one-condenser and the corresponding terminal of the other condenser, a source of direct current polarizing potential for the output electrode of said tube connected to that end of said coil farthest removed from said vacuum tube, and a direct current connection from said source to said metallic surface, said surface being byi passed to ground for energy of frequency.

7. A high power radio transmitter comprising a push-pull amplifier stage comprising a pair of the operating vacuum tubes, a source of radio frequency energy in each side thereof, a condenser from each side of each .of' said networks to a metallic panel, a

, "source of anode direct current polarizing potential for said vacuum tubes connected to the two sides of that pi network nearest the load, a direct current connection from said source of polarizing potential to said panel, whereby said condensers need only be able to withstand the alternating voltage from said amplifier stage, a ground surface behind .said panel, and a radio frequency by-pass condenser coupling said panel to said ground surface.

8. A high power radio transmitter comprising a push-pull amplifier stage comprising a pair of vacuum tubes, a'source of radio frequency energy coupled to the input electrodes of said tubes, a load circuit, and a pair of pi networks in series coupling the anodes of said tubes to said load. each of said networks including an inductor coil in each side thereof, a condenser from each side of each of said networks to a metallic panel, a source of anode direct current polarizing potensides of that pl network nearest the load, a dir t current connection from said source of polari ig potential to said panel, whereby said condensers need only be able to withstand the alternating voltage from said amplifier stage, standoff insulators supporting said induc r coils from said panel, said condensers being mounted on said panel, a ground surface behind said panel, said tubes being mounted on said ground surface. and a radio frequency by-pass condenser coupling said panel to said ground surface. a

,9. A radio transmitter in accordance with claim 6, characterized in this that said metallic surface is a vertical panel which supports said pi network,

10. A high power radio transmitter including a push-pull amplifier stage comprising a pair of triode vacuum tubes, a load, first and second pi networks in series relation coupling the anodes of said stage to said load, the interelectrode capacity of said tube stage constituting the input capacity of said first network, each of said networks including an inductor coil in each side thereof, a condenser connecting each side of each. of said networks at the output end thereof to a common metallic panel, the elements of said networks being supported by said panel, a choke coil across the output end of said second pi network, a source of direct current polarizing potential for the anodes of said tubes connected to the midpoint of said choke coil, and a direct current connection from said source to said panel, said panel being by-passed to ground for energy of the operating frequency.

11. A radio transmitter including a vacuum tube stage, a utilization circuit therefor, a coil coupling the output electrode of said stage and said utilization circuit, a condenser at each end of said coil, a metallic surface connecting together one terminal of one condenser and the condensers and being by-passed to ground for energy of the operating frequency.

12. High power high frequency apparatus comprising a vacuum tube, a high frequency output circuit. comprising an inductor having one terminal connected to the anode of said tube and. another terminal through which anode potential nected to a terminal on said inductor and the corresponding terminal of the other condenser, a

other electrode of which is connected to said metallic panel, asource of direct current potential, a connection from the positive terminal of said source to said inductor for supplying polarizing potential to the anode of said tube, a direct current connection from said source to said panel, whereby the electrodes of said condenser have substantially the same direct current potential applied thereto, and a by-pass condenser connected to said panel and to ground for effectively grounding, said panel at the operating frequency.

13. High frequency apparatus comprising a push-pull amplifier stage, including a pair of vacuum tubes, a source of radio frequency energy coupled to the input electrodes of said tubes, a network including a pair of inductors connected to diiferent output electrodes of said tubes and coupling said tubes to a utilization circuit, a pair of condensers connected in series across a pair of terminals of said inductors, a metallic panel supporting the component parts-of said network, stand-off insulating means supporting said inductors from said panel, each of said condensers having one terminal directly connected to one Y terminal of one of said inductors and the other term nal directly connected to said panel, whereby Said panel forms the electrical junction for said condensers, a source of direct current polarizing potential for the output electrodes of said tubes, direct current connections from said source to said inductors and panel, and a by-pass condenser connecting said panel to ground for high 

